1. Field of the Invention
This invention relates to a power supply system, particularly to a distributed power supply system installed at an individual residence to cover power demand of the residence.
2. Description of the Related Art
A distributed power supply system, i.e., a power supply system of distributed generation (also called on-site generation) is installed near a place where electric power is needed to generate and supply power thereto. Since the supplied power is consumed at the same location as the place it is generated, the system is superior because the power transmission loss can be suppressed. Such a distributed power supply is taught by, for example, by Japanese Laid-Open Patent Application No. 2003-339118.
In the system disclosed in the reference, a DC bus is connected to a wind-power generation unit and photovoltaic generation unit (power generation unit) and to a load (power destination) to supply power generated by the power generation unit to the load, while connected to a commercial power source via a parallel unit so that, when the voltage of the DC bus is decreased upon increase of power demand, power is supplied from the commercial power source.
The system is also connected to a power storage unit and when the generated power exceeds the power demand and the voltage of the DC bus is increased, stores surplus electricity in the storage unit. When the voltage of the DC bus is further increased, the system transmits the surplus electricity back to the commercial power source to sell. Thus, it is configured to efficiently utilize the surplus electricity.